From the time liquid and gaseous fuels came into use for heating, various techniques have necessarily been employed to ignite such fuel. Probably one of the earlier techniques involved using a taper or match for ignition.
Later (and particularly with gaseous fuels such as natural gas), gas-fired combustion equipment used a "standing" pilot light. Such pilot light burned continuously and was instantly available to ignite fuel. Disadvantages of a standing pilot light include unnecessary consumption of fuel, albeit in small amounts, and the practicality of using such standing pilot light only in stationary, permanent installations such as homes and offices.
A more recent innovation involves so-called spark generating circuits which lend themselves well to automatic, e.g., thermostatic, control. That is, when the thermostat calls for heat, early steps in the combustion cycle include opening a pilot valve to allow gas to flow to a pilot light and energizing a spark generating circuit to ignite the raw flowing gas. Such circuits are in wide use today and like heating systems using standing pilot lights, are used mostly in buildings.
Disadvantages of such spark generating circuits include the fact that most are configured to be powered by AC power, Yet another is that they are rather complex circuits and, relatively speaking, expensive. And although of generally modest size, they are physically rather large for applications involving portable heating equipment.
One type of such heating equipment is generally referred to as pressure cleaning equipment or "pressure washers." Such equipment is mounted "dolly-like" on wheels and uses pressurized water, cold or hot, to clean manufactured parts, automobile bodies, building surfaces and the like. The invention is particularly well suited for use with pressure washers.
One rather recent application for such pressure washers involves trucks which indiscriminately carry such diverse cargos as garbage and food products. In the New York City area, it was recently discovered that trucks hauling garbage would, after emptying and without benefit of intervening washing, pick up food products, e.g., fresh produce, for delivery.
It is understood that operators of trucks handling such things as garbage are being ordered to wash such trucks before loading food products. Washing is with hot, high-pressure water from a portable hot water spray machine of the type made by Aqua Blast Company of Decatur, Ind.
Certain patents in the field of spark generating circuits and in other fields are somewhat noteworthy. For example, U.S. Pat. No. 4,918,569 (Maeda et al.) depicts a spark ignition circuit powered from a DC source which is switched on and off as is the nature of power source control in circuits for internal combustion engine spark plugs.
The transformer has but a single primary winding, current to which is switched by a MOSFET. In turn, the MOSFET is controlled by a two-transistor driver circuit. There is also a detector for disabling the circuit based upon load current. Switching the circuit on and off (a necessity of operation) requires additional components and circuitry which, in view of the invention, is not required in other applications.
U.S. Pat. No. 4,329,628 (Bohan, Jr.) involves an AC-powered spark ignition circuit. Such circuit has an energy storage capacitor which discharges through the primary winding of a spark transformer to develop a high, gas-igniting voltage at the transformer secondary. The energy storage capacitor is both charged and discharged during only one-half of the applied AC sine wave. To put it another way, the transformer core is "active" or in use only about one-half of the total operating time.
U.S. Pat. No. 4,414,491 (Elliott) is directed to a power supply for a discharge lamp. Such power supply uses transformer core saturation to control the frequency at which the two-transistor invertor circuit operates. The transformer core has what is described as a shunt flux flow path with an air gap. For certain applications not involving a discharge lamp, the transformer is unnecessarily complex.
An improved igniter circuit overcoming some of the aforementioned problems and shortcomings would be an important advance in the art.